Setting the slicing level or decision threshold level of a receiver in a transceiver at an optimum level is very desirable since a slight offset from the optimum level will degrade significantly the bit error rate (BER) performance of a communication system. The optimum slicing level depends solely on each system in which the transceiver is operating. Here all the communication systems are grouped in three as follows: 1) communication systems without optical amplifiers, 2) optically amplified communication systems, and 3) communication systems using single-wavelength-bidirectional transceivers (SWBiDi).
For the communication systems without optical amplifiers, it is a common practice to use, on a printed circuit board (PCB) of the transceiver without any adjustment, a decision circuit such as a limiting amplifier (LA) whose slicing level is preset (default) in its IC design; the amount of offset from the optimum level is within its IC specification limits though. Considering the cost involved in optimizing the slicing level for the optimum BER performance, a further optimization of the slicing level from the default might not be attractive. As a penalty due to the non-optimum slicing level, these systems must allocate some extra margins in their system link budget where even extra 1 dB of link budget is quite often costly.
For the optically amplified systems, it is well known that the optimum slicing level is shifted from the default level toward the “0” rail due to the beat noises such as signal-amplified spontaneous emission (ASE) beat noise and ASE-ASE beat noises when the optical signal to noise ratio (OSNR) is poor. The amount of shift can be determined only after the BER in the real system is measured at various slicing levels.
For the communication systems using single-wavelength-bidirectional transceivers, it is also known that the optimum slicing level is shifted from the default level toward the “0” rail due to the interferometric beat noise (IBN) when there is reflections along the transmission path. The amount of shift can be determined only after the BER in the real system is measured at various slicing levels.
The transceiver in the optically amplified systems or in the communication systems using SWBiDi requires the adjustability of the slicing level of a receiver in the transceiver because a slight offset of the slicing level from the optimum level might be detrimental for the BER performance of the receiver, effectively making the communication systems unusable. Because a communication system consists of, at least, two transceivers and the receiver of one transceiver is receiving a signal from the transmitter of another transceiver, the controllability of the slicing level of the receiver in one transceiver by another transceiver will be a desirable feature. This is particularly true if two transceivers are physically separated far away from each other. In other words, a remote controllability of the slicing level of one transceiver by another transceiver will be very valuable, considering the facts that 1) the adjustment of its slicing level can be executed by the technician at the central office (CO) where all the necessary test equipments are accessible easily and 2) another technician does not have to be present simultaneously at the site of the transceiver which is in need of adjustment of its slicing level; this will save a lot of capital and operating expenditures (CAPEX and OPEX) by the service provider/operator.